Applications in the millimeter-wave frequency regime have gained significant interest in the past few years due to the rapid advancement in low cost semiconductor technologies such as silicon germanium (SiGe) and fine geometry complementary metal-oxide semiconductor (CMOS) processes. Availability of high speed bipolar and metal-oxide semiconductor (MOS) transistors has led to a growing demand for integrated circuits for mm-wave applications at 60 GHz, 77 GHz, and 80 GHz and also beyond 100 GHz. Such applications include, for example, automotive radar and multi-gigabit communication systems.
In some radar systems, the distance between the radar and a target is determined by transmitting a frequency modulated signal, receiving a reflection of the frequency modulated signal, and determining a distance based on a time delay and/or frequency difference between the transmission and reception of the frequency modulated signal. Resolution, accuracy and sensitivity of the radar system may depend, in part, on the phase noise performance and frequency agility of the radar's frequency generation circuitry, which generally includes an RF oscillator and circuitry that controls the frequency of the RF oscillator.
As the operating frequencies of RF systems continue to increase, however, the generation of signals at such high frequencies poses a major challenge. Oscillators that operate at high frequencies may suffer from a poor phase noise performance that caused by 1/f and thermal noise in the devices that comprise the VCO. Phase noise may be further compromised by non-linear effects of self-bias conditions that affect the gain and tuning characteristics of the VCO.